The present invention relates to a sieve arrangement for cleaning synthetic plastic melts at a high pressure press. More particularly, it relates to a sieve arrangement of the above mentioned type, which has a housing with a throughflow opening forming a part of a flow passage of the high pressure press and a plate or disc provided with several perforations and cyclically displaceable or rotatable in a housing by a drive. At least one of the perforations lies always in the region of the throughflow opening and at least one of the perforations lies always outside the housing, and sieve discs are arranged inside the perforations.
Sieve arrangement of this type are known in the art. One of such sieve arrangements is disclosed in the German document DE-PS 3,443,654. The sieve arrangement described in this document has a rotatable disc located inside the housing and provided with sieve discs in its perforations. Another German document DE-AS 2,153,962 discloses a sieve arrangement in which a displacement plate is arranged in the housing and has perforations provided with sieve discs. The principle advantage of a sieve arrangement is that it allows a continuous exchange of the efficiency of discs and an exchange of strongly dirtied sieve discs. The latter mentioned exchange is performed in that at least one of the perforations and thereby the associated sieve disc is located always outside of the housing and thereby it is freely accessible for an exchange.
In the sieve arrangement disclosed in the German document DE-PS 3,443,654, in the event of dirtying of the sieve disc located in the melt passage and thereby resulting pressure increase in the melt passage, the plate or disc provided with several perforations and the sieve discs in them is somewhat displaced or turned. Thereby a part of the dirtied sieve discs is moved out of the melt passage and a new clean part of a sieve disc can be moved to the region of the melt passage. Thereby a greater, non-dirtied sieve disc portion inside the melt passage is provided and the pressure condition can be normalized. As long as with increasing dirtying again an increase of the melt pressure is detected, a further movement of the plate or disc with the above mentioned effect is performed. This means that the constant maintenance of the pressure in the melt passage can be activated by progressive insertion of non-dirtied sieve disc regions into the melt passage. Those sieve discs which have passed the melt passage are correspondingly dirtied. Basically this dirtied sieve or sieve disc can be exchanged completely and replaced by new or clean sieve or sieve discs.